As used herein the term" bicomponent fiber" means a fiber having at least two distinct, and possibly more, components or domains in intimate adherence along their length. These components are distinct due to the polymer used and/or due to the additives present. The term "filament" means a fibrous strand of indefinite length. The term "staple" means a fibrous strand of short length. The term "fiber" means filaments, staple, or both. The colored bicomponent fibers of the present invention have Munsell Values between about 2.5/ to about 8.5 and Munsell Chromas greater than about/0.5. (Kelly et al, The ISCC-NBS Method of Designating Colors and a Dictionary of Color Names, National Bureau of Standards Circular 553, pages 1-5 and 16 (1955), incorporated hereinto by reference.) The term "colorant" means a solid particulate pigment which may be incorporated into a spinnable polymer to obtain colored filaments.
The incorporation of additives in so-called "neat" thermoplastic polymeric host materials (that is, polymeric materials containing no additives) so as to achieve desired physical properties is well known. Thus, the art has conventionally incorporated colorants, stabilizers, delusterants, flame retardants, fillers, antimicrobial agents, antistatic agents, optical brighteners, extenders, processing aids and other functional additives into polymeric host materials in an effort to "engineer" desired properties of the resulting additive-containing polymeric host material. Such additives are typically added any time prior to shaping of the polymeric material, for example, by spinning or molding (e.g., extrusion, injection, or blow-molding) operations.
The incorporation of colorant additives in filaments formed by melt-spinning a polymeric material has presented unique challenges. For example, the amount of particulate pigment dispersed in a concentrate which is added to the polymeric material must be sufficiently high to impart satisfactory color density, but must not be so high as to interrupt the spinning process. One prior proposal for incorporating colorant additives in thermoplastic polymeric materials is disclosed in U.S. Pat. No. 5,236,645 to Frank R. Jones on Aug. 17, 1993 (the entire content of which is expressly incorporated hereinto by reference).
According to the Jones '645 patent, additives are introduced into a thermoplastic melt by feeding at least one additive in an aqueous vehicle containing a dispersant to form an aqueous additive stream to a vented extruder which is extruding a thermoplastic. The aqueous portion of the aqueous additive stream is thereby volatilized within the extruder and is removed therefrom via an extruder vent. As a result, a substantially homogeneous system containing the thermoplastic, dispersant and the additive is obtained which may thereafter be spun into a filament by melt-extrusion through filament-forming orifices in a spinneret associated with a spin pack assembly.
Some colorants are known to be unsuitable for use with certain polymeric systems--for example, due to degradation of the colorants at the processing temperatures of the polymeric systems, the degradation of the colorants due to the chemical environment of the resin (e.g., reductive nature of many polymeric melts) or the abrasiveness of the colorant per se or a combination of these three phenomena. Thus, it would be highly desirable if synthetic polymeric fibers could be provided which are colored by the incorporation of colorants which, until now, have not been considered potential colorant candidates for such purpose. It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention provides colored bicomponent filaments wherein the colorant is dispersed throughout one of the fiber domains while another of the fiber domains is colorant-free. The colorant-containing component will most preferably occupy between about 10 to about 90% of the fiber cross-section, while the colorant-free domain will occupy between about 90 to about 10% of the fiber cross-section. The colorant-free domain will cover at least about 50% of the fiber's outer surface, and most preferably will cover the entirety of the fiber's outer surface so that it encapsulates or surrounds entirely the colorant-containing domain.